1. Field of the Invention
The invention relates to a supercharging system.
2. Description of Related Art
As one type of supercharging systems used in internal combustion engines, there is a supercharging system that performs supercharging by utilizing exhaust energy. The supercharging system of this type includes a compressor that is installed in an intake passage of the engine, and is operable to pressurize intake air flowing in the intake passage and deliver it into a combustion chamber of the engine, and a turbine that is installed in an exhaust passage of the engine, and operates, due to the momentum of exhaust gas flowing in the exhaust passage, to drive the compressor. Further, the supercharging system of this type may include a bypass passage through which exhaust gas flows while bypassing the turbine, and a waste gate valve that blocks flow of exhaust gas through the bypass passage when it is in a closed state, and permits the gas flow when it is in an open state. Thus, the bypass passage and the waste gate valve are provided for actively controlling supercharging operation of the supercharging system.
As a supercharging system that conducts malfunction diagnosis for determining the presence or absence of a malfunction of the waste gate valve, a supercharging system as described in Japanese Patent Application Publication No. 2014-074386 (JP 2014-074386 A), for example, is known. In the supercharging system in which supercharging is performed utilizing exhaust energy as described above, the boost pressure changes after the rotational speed of the compressor changes according to change of the momentum of flow of exhaust gas and change of the rotational speed of the turbine; therefore, a lag (turbo lag) arises in change of the boost pressure relative to changes in the fuel injection amount and the throttle opening, for example. Thus, in the supercharging system described in JP 2014-074386 A, various parameters, such as the boost pressure, intake air temperature, and the engine speed, are obtained at the time when a fixed transient period elapses from change of a control signal for switching opening and closing of the waste gate valve, and it is supposed that the turbo lag has been eliminated. Then, the intake air amount calculated based on these parameters is compared with a reference value based on data of the intake air amount obtained when the waste gate valve operates normally. If it is found from the comparison that a deviation of the calculated intake air amount from the reference value is within a given range, it is determined that the waste gate valve is in a normal state. If the deviation exceeds the given range, it is determined that there is a malfunction in the waste gate valve.